first year 63
a suckling baby is one of life’s great miracles, so
is the transformation of that wobbly infant into
a walking, talking toddler capable of negotiat-
ing bedtime. While researching this story, I have
watched that miracle unfold before my eyes as
my daughter has gone from a fidgety bundle
with only a piercing cry signaling hunger to a
feisty three-year-old who insists on putting on
her sunglasses before stepping out of the house.
The blossoming of her mental and emotional
abilities has been a string of marvels, deepen-
ing my amazement at how deftly a baby’s brain
comes to grasp the world.
The milestones she has passed would be
recognizable to any parent. At two she knew
enough to realize that she didn’t have to hold
my hand when walking on the sidewalk; she
would reach for my hand only when we were
about to cross the street. Around the same age,
she also learned to block the drain in the bathtub
with the ball of her foot—turning what was to
be a quick shower into a playful bath. Before
she turned three, she was holding lengthy con-
versations and coming up with rhymes: “If the
candy tastes bad, Willy Wonka will be sad.”
Despite millennia of child rearing, we have
only a limited understanding of how babies take
such gigantic strides in cognitive, linguistic, rea-
soning, and planning ability. The lightning pace
of development in these early years coincides
with the formation of a vast skein of neural cir-
cuits. At birth the brain has nearly a hundred
billion neurons, as many as in adulthood. As the
baby grows, receiving a flood of sensory input,
neurons get wired to other neurons, resulting in
some hundred trillion connections by age three.
Different stimuli and tasks, such as hearing a
lullaby or reaching for a toy, help establish dif-
ferent neural networks. Circuits get strength-
ened through repeated activation. The sheath
encasing nerve fibers—made of an insulating
material called myelin—thickens along oft-
used pathways, helping electrical impulses
Natasha Alvarez floats in a swimming hole in Lancaster, Pennsylvania, hoping
that a stress-free pregnancy will help her child’s brain development in utero.
Yudhijit Bhattacharjee is writing a nonfiction book,
The Spy Who Couldn’t Spell. Lynn Johnson’s
feature, “Vanishing Voices,” in the July 2012 issue,
was on the world’s disappearing languages.